This invention relates generally to a unique abrasive blasting apparatus and method for shot peening, or sandblasting, small apertures in workpieces. More specifically, the invention relates to improvements in the design of nozzles employed by such peening devices. With the use of these devices, it is desired to subject the interior wall of an aperture of small diameter to the treatment of sandblasting, or shot peening.
Many modern workpieces have apertures having an extremely small diameters. A turbine manifold used in a jet engine is one example of such a workpiece. The proper operation of such workpieces depends, in part, upon the condition of the workpiece surfaces, including the surfaces of the small apertures, thus making a peening treatment necessary. However, the small sizes inherent in such a peening process present an obstacle to effective peening. Also, the forces present in peening can lead to damage of the workpiece.
In the peening apparatus designs and methods currently available, a straight peening nozzle is aligned with an aperture in the workpiece, so that the nozzle can direct a stream of shot axially into the aperture. To direct the shot against the interior wall of an aperture, a conical or beveled deflector is inserted into the aperture from the direction opposite to that of shot flow. As the shot encounters the deflector, the shot is directed against the interior wall of the aperture. The deflector then is reciprocated within the aperture so that shot encounters all areas of the interior wall of the aperture.
Using the currently available peening methods and apparatuses, problems with the peening process often arose. Because the deflector encountered the direct stream of shot flow, the deflector rapidly wore out. Further, as the deflector wore, the distribution of shot was unpredictable, and inaccurate. Also, pieces of shot could become wedged between the deflector and the interior wall of the aperture. Therefore, when the deflector was translated into or out of the aperture, the interior wall of the aperture would be damaged by the shot being compressed between the deflector and the interior wall, thereby deforming the wall. This was a significant drawback, the adverse effects of which were increased by the practice of reciprocating the deflector within the aperture during the peening process.
Given these adverse effects, and the continued need for subjecting workpieces to the peening treatment, a more effective peening apparatus and method is needed. Because of the small diameter of the apertures in the workpieces, the space in which to work is at a premium. Specifically, a shot peening device, and the method for using that device, must be designed to operate effectively in those close quarters without damaging the workpiece. This is no easy task considering the size of the shot, the diameter of the aperture, the size and configuration of the nozzle which directs the shot, and the accumulation of the shot after the shot has left the nozzle.